Capacitors



United States Patent O "lee 3,113,253 CAPACITRS Yoshoki Ishikawa and Iliichi Okamoto, Tokyo, .lapam .assignors to Nippon Electric Company, Limited, Tokyo,

Japan, a corporation of Japan Filed Aug. 3, 1959, Ser. No. $31,406 Claims priority, application Japan Sept. 22, 1958 2 Claims. (Cl. 317-258) The present invention relates to laminated type capacitors and has for its principal object to provide a capacitor which has a lower leakage current than those heretofore known.

The invention is illustrated in the accompanying drawing in which:

FIG. l is a longitudinal sectional View of a laminated metal film used in making the capacitor of the invention; and

FIG. 2 is a longitudinal Sectional View of a modified laminated metal lilm used in making the capacitor.

The invention utilizes laminating films of different materials comprising a base metal, such as tantalum, aluminum, zirconium, titanium, etc., which is capable of being anodized to form an oxidized lilm, a dielectric film affixed thereupon which is tenacious both mechanically and thermally and is superior in dielectric characteristics, and a metallic film of aluminum, silver, or gold bonded thereto, either directly, or through the intermediary of a semiconductor film or germanium, silicon, lead sulphide, or cadmium sulphide.

In the drawing 1 denotes the base metal foil, possessed of the above-mentioned characteristics and having an oxidized film 2 formed on the surface of said metallic foil 1. A dielectric film 3 of magnesium fluoride (MgFz), calcium lluoride (CaFZ), or silicon oxide (a mixture of SiOz and SiO), which is tenacious both mechanically and thermally and has good dielectric characteristics, is bonded by a suitable method to the oxidized film 2. In the embodiment of FIG. l, a metallic lm 4 of aluminum (Al), or silver (Ag), or gold (Au) is attached to said dielectric ilm 3 directly, whereas in the embodiment of FIG. 2, the metallic iilm 4 is bonded to the dielectric iilm 3 through the intermediary of a semiconductor film 5 of germanium, silicon, or other material. A capacitor may thus be formed by using the base metal foil 1 as anode and the metallic film 4 as cathode. With the above-mentioned construction, the thickness of the dielectric film 3 3,1 13,253 Patented Dec. 3, 1963 should be of the order of 150-100 millimicrons. In spite of the fact that the dielectric property of the oxidized film 2 is poor, the resistance of said dielectric film 3 is high. On the other hand, the thickness of the dielectric lrn 3 can be so adjusted that the resistance of said dielectric iilm 3 becomes much lower than that of the oxidized film 2. As a result, according to one experiment, there was a slight decrease in electric capacity of the capacitor, while the leakage current Was lessened considerably.

With an operating voltage of volts, the electric capacity, loss factor, and leakage current of the conventional capacitor Which does not have the above-mentioned dielectric film 3 were 0.04 ,al1/cm?, 5% (tan (both measured at 1 kc), and 1.0 ,aa/FV., respectively. These values for the capacitor in accordance with this invention are found to be less than 0.035 f./cm.2, 5%, and 0.7 pla/MFV., respectively.

While I have described above the principles of my invention in connection with specific apparatus, it is to be clearly understood that this description is made only by way of example and not as a limitation to the scope of my invention as set forth in the objects thereof and in the accompanying claims.

What is claimed is: y

l. A capacitor comprising in combination a base metal foil, an oxide film formed on the surface of said foil, a ilm of mechanically and thermally tenacious dielectric selected from the group consisting of magnesium lluoride, calcium fluoride and silicon oxide on said oxide film, and a metallic film on said dielectric iilrn.

2. A capacitor comprising in combination a base metal foil, an oxide film formed on the surface of said foil, a ilm of mechanically and thermally tenacious dielectric selected from the group consisting of magnesium lluoride, calcium fluoride and silicon oxide on said oxide iilm, a semiconductor film on said dielectric film, and a metallic film on said semiconductor film.

References Cited in the le of this patent UNITED STATES PATENTS 1,900,018 Lilienfeld Mar. 7, 1933 1,906,691 Lilienfeld May 2, 1933 2,504,178 Burnham Apr. 18, 1950 2,593,829 Arledter Apr. 22, 1952 2,614,524 Haynes Oct. 2l, 1952 2,734,478 Reynolds et al Feb. 14, 1956 

1. A CAPACITOR COMPRISING IN COMBINATION A BASE METAL FOIL, AN OXIDE FILM FORMED ON THE SURFACE OF SAID FOIL, A FILM OF MECHANICALLY AND THERMALLY TENACIOUS DIELECTRIC SELECTED FROM THE GROUP CONSISTING OF MAGNESIUM FLUORIDE, 